1. Field of the Invention
This invention relates generally to Physical Vapor Deposition (xe2x80x9cPVDxe2x80x9d) systems, and more particularly to an apparatus and method for improving film uniformity in a PVD system.
2. Description of the Background Art
Physical vapor deposition (xe2x80x9cPVDxe2x80x9d) is a well known technique for depositing metal layers onto semiconductor wafers (also referred to herein as xe2x80x9csubstratesxe2x80x9d). These thin metal layers can be used as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, and etch stops, etc.
In a conventional Hollow Cathode Magnetron (xe2x80x9cHCMxe2x80x9d), magnetic fields are used to generate a high density plasma of Argon (xe2x80x9cArxe2x80x9d) or other suitable inert gas and target material within a cathode of the HCM. The magnetic fields are also used to confine the plasma within the HCM. The cathode also has a target, such as Tantalum (xe2x80x9cTaxe2x80x9d), Aluminum (xe2x80x9cAlxe2x80x9d), Titanium (xe2x80x9cTixe2x80x9d), or other suitable metal. A power pin supplies a negative potential to the target such that the magnetic fields in combination with the negative potential cause plasma ions to hit the target with high energy, which in turn cause target atoms to dislodge from the surface of the target by direct momentum transfer and also create secondary electrons. These dislodged atoms and ions (created by the secondary electrons) are then deposited on the semiconductor wafer.
To decrease the cost of manufacturing, the semiconductor device industry is migrating from 200 mm wafers to 300 mm wafers. However, this increase in wafer size brings with it associated problems relating to film uniformity. Specifically, PVD systems that may be suitable for 200 mm wafers significantly increase edge roll-off when used to process 300 mm wafers, such that on average the film deposition is 10% thicker at the center of the substrate than at the edges. In addition, Rs uniformity, film thickness uniformity and step coverage uniformity are also decreased significantly with the 300 mm substrate.
Accordingly, a PVD system that can be used to perform PVD on varying wafer sizes, including 300 mm wafers, is highly desirable.
The present invention provides an apparatus for improving film uniformity in a PVD system. In one embodiment, the apparatus comprises a plasma downstream control mechanism for use in a HCM. The plasma downstream control mechanism comprises three EM coils in the HCM. The three coils are spread between the HCM target mouth and the pedestal, on which the substrate is located. In one embodiment, the top coil has the strongest amp-turn and middle and lowest coils have successively decreasing amp-turns. These three coils form a convergent tapered magnetic lens, which gradually confines the plasma leading to more uniform target ion and neutral distributions. This, in turn, leads to a more uniform vapor deposition on the substrate with improved Rs uniformity, film thickness uniformity and step coverage uniformity across a wafer substrate.
The present invention further provides a method for improving plasma and film uniformity in a PVD system. The method uses the apparatus described above and comprises the steps of maintaining a plasma within the cathode of the HCM and using the plasma downstream control mechanism to control the flow of ionized target atoms onto the wafer substrate.
The system and method may advantageously perform PVD onto a wafer substrate, including 300 mm wafers, yielding an improved Rs uniformity, film thickness uniformity and step coverage uniformity as compared to a conventional PVD system.